A coarse-grained particle simulation on the capillary suspension and its rheological properties under the simple shear flow

Abstract

A capillary suspension is a ternary system consisting of one solid and two immiscible liquids. As a small amount of one of the fluids, also known as the secondary fluid, is present in between the particles to form a sample-spanning network, the suspension experiences dramatic changes in the rheological properties. In this paper, a particle simulation on the capillary suspension is proposed by introducing the coarse-grained interaction between fluid droplets and solid particles. The shape of the free surface between two fluid phases is assumed as a sphere, which can be partially superposed on the solid surface, while the volume occupied by the fluid droplet is preserved. By using the method, the formation of the capillary suspension is simulated under various conditions to achieve a sample-spanning network. The structure and flow properties of the capillary suspension are investigated at the size ratio of 0.4 and secondary fluid concentration of 2 vol%. Under low dimensionless shear rates less than 0.5, the simulated flow properties show a sign of local freezing, and the local properties of the frozen zone are isolated from the bulk properties and further investigated. The local stress increases linearly with the local strain in the frozen zone, exhibiting an elastic behavior. This indicates that the material preserves its structure over the imposed strain, and the difference between imposed and apparent strain is interpreted as the effect of yield stress. Finally, the yield stress is calculated as 5.7 in dimensionless form, similar to that reported in previous studies.